Regarding leaching methods for recovering copper from a layer of ores, following two methods have been generally known; one is a heap leaching method, comprising agglomerating the ores whose particle size is adjusted, heaping the agglomerates on a high-density polyethylene sheet to an adequate height, and supplying acid over the heap, and another is a dump leaching method, comprising piling the adequately crushed ores, and irrigating leaching solution thereover. However, the most of ores applied in the commercial operations using such leaching methods are limited to copper oxide ore because copper sulfide ore is poorly soluble in mineral acids.
Meanwhile, among copper sulfide ores, chalcocite and bornite are relatively soluble in a moderate acid containing Fe3+ or the like. Therefore, heap leaching or dump leaching relative to such ore has been commercially operated in some cases. However, the copper recovery becomes low if the ores to be leached contain poorly soluble copper sulfide ores, such as chalcopyrite.
Hence, a variety of techniques have been suggested in order to increase the leaching rate when a copper sulfide ore with a higher chalcopyrite content is subjected to heap or dump leaching with the use of a mineral acid. For instance, a leaching method comprising adding activated carbon to a leaching solution (JP Patent Publication (Kokai) No. 2007-204830 A) and a leaching method comprising adding sliver as a catalyst (J. A. Munoz, D. B. Dreisinger, W. C. Cooper, S. K. Young, Hydrometallurgy, 88, 35 (2007)) have been reported. However, such methods are problematic in terms of environmental burdens and high costs, although these methods are effective for the improvement of the leaching rate. Therefore, neither method has been used in practice.
Meanwhile, it has been known that physical factors significantly affect heap or dump leaching. For example, the total recovery of leached copper and the leaching rate of copper are influenced by whether the irrigated leaching solution is effectively and evenly distributed in the ore layer or not. When a flow channel of the leaching solution is fixed by a phenomenon of “channeling phenomenon”, the leaching of copper from the layer of the ore is limited in sites along the fixed flow channel. In order to reclaim and to avoid this phenomenon, a step of irrigating a leaching solution with a sprinkler and a step of setting the resting period of solution supply can be applied. However, none of these steps are sufficiently effective.